I have perpetual PT 10/11 license. Should I buy 599USD perpetual license (again) to get perpetual upgrade to PT 12? I need a perpetual upgrade, not 1-year license.

Probably this info is out there somewhere, but I can't find it ;-/ All I find is either perpetual license for those buying for the first time, or 1-year update (I gather after one year I would be reduced to my previous PT 10/11 perpetual license?).

You can upgrade from PT11/10 to PT2019 as PT12 is not sold anymore. When The yearly support plan expires you will have a perpetual license of the last PT version out before expiration i.e if your 1 year expires at PT 2020.0 for example your perpetual license will activate the last version when you stop paying.

The price would be $299 as the $599 is the same but more expensive as that version is for people with no PT version to update from.